This invention relates to woodworking benches and means for temporarily fixing workpieces to such benches.
A wide variety of fixtures and devices for temporarily fixing a workpiece to a woodworking bench have been developed over the years. Among them are hold-downs that press the workpiece against the workbench top or, in some instances, an edge or side of the workbench.
Perhaps the oldest such hold-down, sometimes known as a "classic" hold-down, consists of a single-piece metal apparatus having a straight round post and a gooseneck that extends out and down from the post to terminate in a foot that presses against the workpiece. The post is inserted in a hole in the workbench top and tapped so that the post cocks within the hole in the top as the gooseneck is flexed to apply pressure on the workpiece. The principal disadvantage associated with this type of hold-down is the difficulty of controlling it. It is very difficult to obtain controlled clamping pressure because such a fixture must be manipulated with a hammer. Additionally, use of such a hold-down over time enlarges the hole in the bench at the top and bottom because of repeated impact and wear of the post against the bench hole into which it fits.
A second type of bench hold-down or "holdfast" has a post that is received in a collar that must be permanently mortised and fixed into the workbench top. Ribs cast into the inside of the collar mate with ribs cast on one side of the post in order to prevent its withdrawal from the collar during use. A hold-down arm terminating in a pivotable foot is itself pivotably mounted on a projection from the top of the post and may be adjustably pressed against a workpiece by the action of a handscrew journaled through the end of the arm opposite the foot so that the screw bears against the top of the post causing the arm to pivot down as the screw is advanced. This type of hold-down permits more easily adjusted clamping pressure than the classic hold-down but can be used only where the required mating collar has been mounted in a workbench.
A third type of hold-down is similar in appearance to one-half of a conventional cast iron C-clamp, including the clamping screw but with a body that terminates in a foot that rests against a workbench top and is held in place by a bolt mounted in the bench top. The clamping capacity of this type of hold-down is limited by the length of the clamping screw and height of the clamping body and typically approximates only three to four inches. Additionally, clamping pressure can be applied only to a portion of a workpiece close to its edge because the reach of this type of hold-down is very limited. Like the pivoting hold-down described above, the clamping type of hold-down can be used only in positions where the securing fixture or bolt have been located in a workbench.
A fourth type of hold-down, somewhat similar to the clamp-type described above, substitutes a smooth round post for a portion of the clamp body, which post is received in a hole in the workbench top. Because the post is smooth, it is held in place solely by the limited friction between the post and the sides of a hole in the bench top, and the post must tilt in order to do so. As a consequence, however, it works well only with relatively thin bench tops that have hole diameters adequate to permit the desired tilt. Such hold downs will not work at all, however, if the hole is too large because the post will simply slip within the hole. Additionally, because the arm in this type of hold-down is rigidly fixed to the post, advancing the screw that applies force against the workpiece through a pad or foot on the end of the screw tends to cause the substantial friction between the foot and the workpiece to resist further canting of the post in the workbench top hole. This can cause the post to slip in the workbench.